1. Field of the Invention
The present invention relates to a machine that includes a motor including a brake.
2. Description of the Related Art
A machine, such as an industrial robot, machine tool or the like, includes a drive axis for moving a member in a predetermined direction. For example, the robot includes a drive axis for driving an arm. A joint unit between arms of the robot corresponds to the drive axis. A change in angle between the arms at the joint unit causes a change in position and posture of the robot. Further, in the machine tool, a workpiece and a tool are moved on a predetermined drive axis, so that the position of the tool with respect to the workpiece is changed.
Such a member that moves on the drive axis is driven by a motor. The motor is provided with a brake to prevent rotation of an output shaft of the motor. When power supply to the motor is interrupted, the brake operates to maintain the position and posture of the robot or the position and posture of a tool or table of the machine tool.
Japanese Patent No. 5444421 discloses a brake abnormality diagnosis method for diagnosing an abnormality in a brake for a motor provided in a robot. In a state in which the motor is excited and the brake is operating, there is a case where it is diagnosed that there is an abnormality in the brake. In this brake abnormality diagnosis method, when it is diagnosed that there is an abnormality in the brake, the abnormality in the brake is notified without interrupting the excitation of the motor and releasing the brake.
An example of a drive axis on which gravity acts includes the drive axes of the machine. For example, the drive axis of the joint unit of the arm of the robot is subjected to a force with which the arm is moved downward in a vertical direction due to the weight of the arm. When the brake fails, the braking force of the brake is decreased. For example, when a material such as grease or oil adheres to a friction plate of a brake included in a motor, the braking force of the brake is decreased. When the braking force of the brake is decreased, there is a case in which the drive axis on which gravity acts is actuated when the excitation of the motor is interrupted.
In particular, when a situation occurs in which the robot or the like should be stopped urgently so that an emergency stop of the robot is performed, the excitation of the motor is interrupted. However, when the brake is in failure, there is a case in which the posture when stopped can no longer be maintained so that the position of a part of the arm is lowered.
In the method disclosed in the above Japanese Patent No. 5444421, it is possible to regularly perform abnormality diagnosis in a state in which power is supplied to the motor. However, when the brake is in failure immediately after no abnormality is detected in regular diagnosis, the power supply to the motor would be interrupted, and therefore, there would be a possibility that the position and posture of the robot is changed.